This invention relates to an image data conversion processing device for converting into television signals image data which are developed in plural kinds of developing formats in a memory, and an information processing device having the image data conversion processing device.
The information processing device comprises a personal computer including a memory and a processing unit, for example. The information processing device is connected to a cathode ray tube (CRT), and image data output from the memory is displayed on the CRT. At this time, the image data is developed in various kinds of developing formats into a video random access memory (VRAM).
The image data comprises 320 picture elements (dots) on each line, and the total number of lines is 200. Alternatively, the image data comprises 640 dots×400 lines or 640 dots×480 lines. The frame (screen) of the CRT is divided into a display frame area for displaying the image data and a non-display frame area.
A program has mode data corresponding to an image mode of the image data for displaying the image data on the screen. The mode data represents the size of the non-display frame area, the number of dots of the display frame area in a horizontal direction, a flyback period and a read-out frequency for each dot.
A device for controlling the CRT to display the image data serves to set a horizontal scanning frequency 31 KHz on the basis of the mode data of the program when the image data comprises 640 dots×480 lines. This device reads out the image data at a read-out frequency 28 MHz from the VRAM in accordance with the set horizontal scanning frequency. The CRT displays the image data on the display frame area thereof on the basis of the mode data.
On the other hand, this device sets a horizontal scanning frequency of 15 KHz when the image data comprises 320 dots×200 lines. In this case, the device reads out the image data at a read-out frequency of 21 MHz from the VRAM in accordance with the horizontal scanning frequency. Further, the device sets a horizontal scanning frequency of 24 KHz when the image data comprises 640 dots×400 lines. In this case, the device reads out the image data at a read-out frequency of 25 MHz from the VRAM in accordance with this horizontal scanning frequency. Various CRTs are individually provided in accordance with image data which are developed in various kinds of developing formats.
As described above, the device for controlling the CRT to perform its display operation enables the CRT to display image data corresponding to the image mode by setting a horizontal scanning frequency.
In addition, a multi-CRT capable of displaying various image data of 320 dots×200 lines, 640 dots×400 lines and 640 dots×480 lines for example has been recently proposed. In this case, an information processing device having the program outputs a composite signal to the multi-CRT. The composite signal comprises horizontal synchronizing signal and a vertical synchronizing signal of 31/24/15. On the basis of the composite signal, the multi-CRT displays image data of RGB signals which are output from the information processing device.
On the other hand, there is a television device which is generally used for a domestic purpose in contraposition with the CRT and the multi-CRT as described above. The horizontal scanning frequency of this television device is specified to 15 KHz (accurately 15.73426 KHz), and an effective line number is specified to 400 lines. In the television device, one frame is displayed with two fields through an interlaced scanning operation in which the frame is scanned with interlacing lines.
It has been increasingly required that this type of television device is connected to the information processing device to promote the propagation of the information processing device. In this case, a scan converter for converting image data into a television signal is required. The scan converter is provided with a change-over switch for selecting any one of the plural horizontal scanning frequencies as described above, and on the basis of a set (selected) horizontal scanning frequency the scan converter converts the image data to be displayed by the information processing device. The television device displays an image on the frame thereof on the basis of the television signal.
As described above, when the television device is connected to the information processing device, the scan converter converts image data transmitted in an analog form into digital signals and then stores the digital signals into an internal VRAM. Further, the scan converter converts the image data to television signals which will be interlaced at a horizontal scanning frequency 15 KHz, and output the converted television signals to the television device.
When the line number of image data to be developed in the VRAM exceeds 400 lines of a television frame, the conventional scan converter displays only an image portion corresponding to 400 lines, which is specified by an adjusting volume. Therefore, in this case, a problem occurs in that the other image data corresponding plural lines other than the above 400 lines is not displayed on the television frame (screen). In order to solve this problem, the image data is compressed by the scan converter.
If the image data is uniformly compressed by the scan converter, an image which should not be compressed might be compressed. For example, the information processing device frequently outputs image data of 640 dots×480 lines and image data of 640 dots×420 lines at a horizontal scanning frequency 31 KHz, for example. In this case, the image data of 640 dots×420 lines can be displayed on the television screen, whereas the image data of 640 dots×480 lines cannot be displayed on the television screen.
The scan converter serves to compress the image data of 640 dots×480 lines to 640 dots×420 lines at a constant compression rate, however, it also compresses, at the constant compression rate, the image data of 640 dots×420 lines which is originally unnecessary to be compressed.
Further, use of the scan converter as described above induces a problem that a user must select a horizontal scanning frequency through the change-over switch. The composite signal may be used to remove a user's manipulation of the change-over switch. The composite signal is a synchronizing signal, and comprises signals having respective frequencies. In this case, code information representing each of the frequencies is not transmitted. Thus, the frequency cannot be immediately identified on the basis of the composite signal. Accordingly, for example, a frequency detector for detecting each frequency is provided to the scan converter. The manipulating operation of the change-over switch can be omitted by using a detection result of the frequency detector. However, in this case the circuit construction of the scan converter is more complicated.
Further, when the scan converter is used, the image data to be displayed, which is developed in the information processing device, is converted from a digital signal to an analog signal. Then the analog signal is re-converted to the digital signal again by the scan converter. As a result, a problem occurs in that the image quality of the image data to be displayed on the television device is deteriorated.
Still further, in the conventional scan converter, the image data transmitted from the information processing device is converted to the television signal merely through the interlaced scanning operation. Therefore, a flicker occurs on the screen of the television device, and consequently, a displayed image is obscure.